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The last time Eyjafjallajökull erupted: an account from 1822 5 May 2010

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[From the Liverpool Mercury, 13 September 1822, p. 86.]

Eruption of the old volcano of Eyafjeld Jokkul in Iceland, in December 1821

The remarkable fall of the barometer which took place almost simultaneously throughout all Europe, in the month of December, 1821, and which in some cases was accompanied with an agitation of the magnetic needle, brought many persons to conjecture that some tremendous convulsion of nature must have visited some part of the globe. This conjecture has at last been verified by a volcanic eruption of the old volcano of Eyafjeld Jokkul, which has been in a quiet state since the year 1612.

This mountain, otherwise called Mount Hecla, is about 5666 feet in height. It is nearly equidistant from Kolla and Hecla, and is the southernmost of the chain where a dreadful eruption broke out about the middle of the last century.

On the 19th December, 1821, the eruption began. The crater was formed at the distance of five miles from the minister’s house at Holt, and discharged itself through the thick mass of ice that enveloped it, and which is never melted. The ice was dispersed in every direction, of which one mass, 18 feet high, and 60 feet in circumference, fell towards the north. A number of stones, of different sizes, rolled down the mountain, accompanied with a noise like thunder; and this was immediately followed by a discharge of an enormous and lofty column of flame, which illuminated the whole country, and allowed the people in Holt to read as perfectly within their houses at night as if it had been day. Ashes, stones, gravel, and heavy masses of rock, some of which weighed about 50 lbs, were thrown up, and one of these last was found at the distance of five miles from the crater. On the day immediately following the eruption, a great quantity of fine greyish-white powder of pumice was discharged, and carried about by the wind so as to fall like snow, through every opening. It exhaled a disagreeable smell of sulphur, brought on affections in the eyes, and occasioned diseases among the sheep in Vaster Eyafjeld and Oster Landoe.

On the 25th of December, a violent storm raged from the south, and by the united action of the wind and rain, the fields were cleaned of the sulphurous dust which had covered them. On the 26th and 27th of December, there was a heavy storm from the north-east, and the barometer, which had been gradually falling since the 18th December, when it was 29° 16, had reached, on the 26th December, its lowest point at 28° 49. It is a curious fact, however, that on the 8th of February, the barometer fell to 27° 25, a time when no earthquake was felt, and no apparent change had taken place in the eruption. On the 18th of February, the barometer, which had been at 29° 42 on the 11th fell to 27° 72. So late as the 23d of February, the Eyafjeld Jokkul emitted smoke greatly resembling the steam of boiling water; and some persons were of the opinion that the mountain had decreased, and was lower near the crater, as it evidently appeared to be when viewed in a direction from north to south.

It is stated that the water in the rivers that flow from the Jokkul and the surrounding mountains, had been considerably enlarged during the first day’s eruption. A constant rumbling noise was heard in the vicinity of the volcano, attended occasionally by a dreadful crash, as if the immense masses of stones and ice were on the eve of all being precipitated down the mountain.

Other two volcanoes to the east, in the mountains of Kolla and Oraefa Jokkul, are said to have broken out, but no certain information has been received on that subject.

The vessel which brought the account of the volcanic eruption to Copenhagen, left Iceland on the 7th of March and it is reported that the sailors, when at sea, again saw a violent fire in the direction of the volcano.

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Stromboli from the inside, 1933 style 16 February 2010

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I realized clearly the danger confronting me as I slipped over the edge of the crater and was lowered slowly into space. I knew my return was problematical. My precautions might prove insufficient. My heart and lungs might not stand the strain of the gases and the terrific heat. Suspended in space, I knew not where I was going nor where I would set down my feet. What awaited me at the end of my descent? Solid rock? Boiling lava? A sheer, slippery ledge with fire below? I could not tell.

Don’t you miss the days when science was an adventure and scientists were heroes, or maniacs, or both? When volcanology meant being lowered 800 Feet on a Fireproof Rope Inside a Flaming Volcano?

[From the highly-recommended Modern Mechanix blog.]

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Goethe’s volcanoes 15 December 2008

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Heinrich Christoph Kolbe, 'Goethe as poet and artist before Vesuvius' (1826), detail. Thuringian University and State Library, Jena.

Goethe Etc. (proprietor: Goethe Girl) is a wonderful scholarly blog exploring the life, work and significance of Johann Wolfgang von Goethe (1749-1832). It features here because, among many other things, Goethe was interested in volcanoes, and when he visited Naples in 1787 during his Italian journey he took the opportunity to study, observe and ascend Vesuvius. The significance of Vesuvius to Goethe’s developing poetic and visual imagination is considered in Goethe and Vesuvius, a fascinating illustrated essay at Goethe Etc.

At the time of Goethe’s visit the British envoy in Naples was Sir William Hamilton, who was also greatly interested in volcanoes. Hamilton, however, was a ‘plutonist’, believing that volcanic action had deep-rooted causes and was a permanent and fundamental geological process, while Goethe espoused the ‘neptunist’ view that volcanoes were superficial phenomena of no profound geological significance.* This aspect of Goethe’s thought is discussed in Goethe and Vesuvius and also in another article at Goethe Etc., Goethe in Bohemia, which illuminates Goethe’s geology.

* Despite their different theories of volcanism Goethe rather admired Sir William, and definitely admired his wife, the (in)famous Emma.

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Aesthetic geology – Sir William Hamilton’s ‘Campi Phlegraei’ 14 June 2008

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[This article is written as a contribution to Accretionary Wedge #10, ‘Aesthetic Geology’, which is being hosted by Geological Musings in the Taconic Mountains.]

For an article addressing the topic ‘aesthetic geology’ it seems appropriate to look at what is certainly one of the most aesthetically beautiful geological works ever published: Sir William Hamilton’s Campi Phlegraei: Observations on the Volcanos of the Two Sicilies (1776).

Sir William Hamilton (1730-1803), perhaps best-known today as the husband of Emma Hamilton, mistress of Admiral Lord Nelson, was in his own right a skilled diplomatist, a celebrated connoisseur and collector, and a respected natural historian. In his own time he was honoured in particular for his contributions to the study of volcanoes, acquiring the title ‘the modern Pliny’ for his studies of Vesuvius.

Campi Phlegraei (1776) - plate III, view of Naples

Above: Campi Phlegraei, plate III, a view of Naples. This view shows Naples and Vesuvius as a harmonious whole, with traffic on the road and vessels in the bay serving to illustrate the place of the volcano as part of the city’s daily life. The figures reacting to their surroundings draw the viewer in and emphasize the importance of an active engagement with the landscape.

Hamilton arrived in Naples as British envoy to the Neapolitan royal court in 1764, and became fascinated by Vesuvius. Shortly after his arrival the volcano went into an eruptive phase that lasted until 1767, giving Hamilton ample opportunity to observe and report upon its behaviour. In 1766 he was elected a Fellow of the Royal Society and the core of his volcano studies was contained in a series of letters written to be read aloud at the society’s meetings and published in its Transactions. It was these letters that were collected together into one volume as Campi Phlegraei in 1776. The text was accompanied by fifty-four lavish illustrations, prepared by the artist Pietro Fabris under Hamilton’s direction, and hand-coloured. The resulting volume was very expensive to produce, and placed a great deal of strain upon Hamilton’s always fragile finances, but has become celebrated as one of the great monuments of eighteenth-century science.

Campi Phlegraei (1776) - plate VI, view of the 20 October 1767 eruption of Vesuvius

Above: Plate VI of Campi Phlegraei shows the eruption of 20 October 1767. On the left is the harbour breakwater or mole of Naples, with its lighthouse, and shipping in the harbour. A lava flow is spreading as it descends the flanks of the volcano towards the sea; lightning is visible in the eruption cloud. This night-time view of Vesuvius is one of the most dramatic illustrations in Campi Phlegraei, with the volcano as a grand and sublime object. Yet the peaceful harbour in the foreground suggests that the works of man can co-exist with the volcano.

Hamilton believed passionately in the importance of careful, direct observation of natural phenomena, and Campi Phlegraei is intended to make the various aspects of Vesuvius’s activity available to those unable to see the volcano directly themselves. He ensured that Fabri’s illustrations were as accurate and detailed as possible, reflecting his aim of offering ‘accurate and faithfull observations on the operations of nature, related with simplicity and truth’. The desire to view phenomena directly for oneself, and to form one’s own opinion on the basis of the evidence, can be seen as a central principle of the Enlightenment.

Campi Phlegraei (1776) - plate XII, 1760-61 eruption of Vesuvius

Above: Plate XII of Campi Phlegraei is a dramatic scene of advancing lava flows from the eruption of December 1760 to January 1761. Hamilton used the original caption of this image to argue against those who believed that the seat of a volcano’s ‘fire’ was always near the summit.

One of the fundamental debates of eighteenth-century geological study was whether volcanoes represented peripheral or central phenomena in the structure and workings of the Earth. ‘Neptunists’ argued for the sedimentary origin of all rocks and believed volcanoes were the superficial result of localized combustion, having no geological significance; ‘Plutonists’ saw heat as the most important agent in the history of the planet, with volcanoes as an essential expression of its operation. Hamilton’s observations of Vesuvius, and his reading of the surrounding landscape in terms of the volcanism of the past, led him to the conclusion that volcanoes were a central geological phenomenon, based on a deep-seated heat source, and that there had been volcanic action throughout the history of the Earth. He also saw volcanic action as a positive, creative principle, producing fertility, reshaping the landscape, an agent of re-creation rather than destruction. The illustrations in his Campi Phlegraei convey the grandeur and power of the volcano, but also seek to embody and convey these ideas: they aim to communicate information as well as to inspire wonder. They are an expression of a new scientific aesthetic.

David Constantine, Fields of Fire: A Life of Sir William Hamilton (London: Weidenfeld & Nicolson, 2001)
Ian Jenkins & Kim Sloan (eds.), Vases and Volcanoes: Sir William Hamilton and his Collection (London: British Museum Press, 1996)
Joachim von der Thüsen, ‘Painting and the rise of volcanology: Sir William Hamilton’s Campi Phlegraei, Endeavour, vol. 23, no. 3 (1999), pp. 106-109
Karen Wood, ‘Making and circulating knowledge through Sir William Hamilton’s Campi Phlegraei, British Journal for the History of Science, vol. 39, no. 1 (March 2006), pp. 67-96

Sir William Hamilton, Campi Phlegraei – Glasgow University Special Collections Department
Sir William Hamilton, Campi Phlegraei – Georgetown University/Campania Libraries
Campi Phlegraei – from the Science Museum Library

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The latest volcanoes in the British Isles – a lecture from 1895 3 June 2008

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[From The Liverpool Mercury, 26 December 1895, p. 2]

The presidential address in connection with the Geological Society of Glasgow was delivered by Sir Archibald Geikie, the Director-General of the Geological Survey of Great Britain.

Sir Archibald Geikie said his first duty was to thank the members of the Geological Society for the honour conferred upon him some time ago in electing him their president. He had a keen interest in the society. It was now more than 30 years since that connection began, and one of his earliest papers was published in the first volume of their transactions. Although he had no prepared address to deliver to them that night, he proposed to speak to them on a subject that had occupied him closely for the last 20 years, and more particularly the last seven — the story of the last volcanoes in eruption in the British Isles. Our islands were especially fortunate in the wonderfully complete record which we had within our borders of the history of volcanic action, and these were nearer than the time of the soft clays on which London was built. There was an almost continuous line of volcanic eruption along the western border of the European Continent. Our country was placed on what one might call the critical line of the European Continent. He proposed to sketch rapidly the story of the last volcanoes. These were active along the great line of valleys between the Outer Hebrides on the west and the mainland of Scotland on the east, and they extended from the South of Antrim right through that hollow, through the line of the Inner Hebrides, and on to the Faroe Islands. During the last two years he had been able to extend his researches amongs those rocks in the Faroe Islands, and he had been specially interested to find that the story of volcanic action was told there even more fully and more clearly than it was within our own islands, a result partly due to the difference of climate, greater denudation, and the greater height. The Icelandic geologist — for there was really only one — complained that geologists in their text-books and in their memoirs had been in the habit of quoting Etna and Vesuvius as types of volcanic action, and pointed out that in Iceland they would find the most potent forms of volcanic activity. He sympathised with that geologist, for he found that the story of our own volcanic history was more clearly made known by the study of the Icelandic volcanoes. One of the first features that struck them in looking at the history of the modern Icelandic volcanoes was that they did not form mountains like Etna or Vesuvius, but were the production of great fissures. When a volcanic eruption was to take place the ground seemed to have been rent into long, rectilinear fissures, of which two series at least had been discovered — one running in a north and south line, and the other running from south-west to north-east. In some cases the lava had risen up through these fissures, and flowed out tranquilly now to one side and now to the other. Most frequently it happened, however, that the lava formed great long lines of volcanic cones so close together that they actually touched each other. From the base of these cones the lava streams flowed now to the one side and now to the other, and solidified over the surface. As each eruption occurred the surface was again covered over, and so altered the topography of the country. In some cases the intervals between the outpourings of lava would be very considerable, and along the western coast of Skye and the west of Mull there was found a red layer with one of dark, almost black, rock on the top of it. Sir Archibald Geikie referred to the fact that last year, when yachting among the Western Islands, he discovered some new facts of considerable importance in considering the volcanic action in that region. Last year he also visited the Faroe Islands, and was able at one part to trace distinctly no less than five old volcano vents which had been completely buried by about six, eight, or perhaps even ten thousand feet of volcanic material. He also referred to a visit which he was able to pay to St. Kilda this year, and to get to the junction of the two masses of rock. He found the black gabbro riddled with a network of fine light-coloured rock, such as was found in Mull of Skye and Rum, but on a much larger and grander scale than in any of these islands. He hoped to be able to make a more thorough examination next year, if the weather would permit him. The volcanic period of which he had been speaking belonged to a very recent geological period — and belonged to a time actually later than the soft clay on which the city of London was built. He concluded by referring to the interesting shores of the Faroe Islands, where the imagination, which was apt to be carried away by the contemplation of scenery so splendid, was always checked by those solemn, unmoved lines always in front of them, and where they could actually obtain numerical data to control them. (Applause.)

Sir Archibald Geikie (1835-1924) – biography from NAHSTE
Sir Archibald Giekie (1835-1924) – another biography from Scottish Geology
Sir Archibald Geikie, The Scenery of Scotland (1887) – an online edition prepared by Dr David C. Bossard
Geographical Evolution: An Introduction – text of an 1879 lecture by Geikie

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Capelinhos 1957-8: fifty years on 12 April 2008

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Fifty years ago, between September 1957 and October 1958, a dramatic submarine eruption took place on Fayal island in the Azores. Fayal itself is a large stratovolcano with a wide caldera; the eruption took place on the west flank of the volcano, beginning at a point about 1 kilometre west of what was then the westernmost point of the island, and created the volcanic cone of Capelhinos which began as an island and is now a peninsula.

The eruption was one of the most closely-studied in the history of volcanology. It was also highly disruptive for the island’s population: vast amounts of ash were erupted, agriculture was ruined, hundreds of homes destroyed or rendered uninhabitable, and the economy of the island severely damaged. More than 2000 people were evacuated, many to begin new lives in the United States, where a sizeable Portuguese-American population traces its origins to the eruption and the subsequent relief effort today.

The story of Capelinhos is thus not only a scientific story but a profoundly human one as well. The fiftieth anniversary of the eruption is being marked in the Azores and mainland Portugal, and in the United States, with events and publications that reflect all aspects of this historic event.

Smithsonian Institution Global Volcanism Program – summary information for Fayal (1802-01=)
Observatório Vulcanológico e Sismológico da Universidade de Açores – responsible for monitoring volcanism in the Azores (Portuguese)
Vulcão dos Capelinhos – website of the official commemorative commission for the Capelinhos fiftieth anniversary, in English (the Portuguese site is here)

Fifty years ago, a volcano changed everything – report from EastBayRI.com on the Capelinhos eruption and the evacuation, which brought many Azoreans to Rhode Island
Erupção do Vulcão dos Capelinhos foi há 50 anos – report on the anniversary from Rádio e Televisão de Portugal (Portuguese)
U.S.-Portugal relationship analyzed at Brown University – report from the U.S. newspaper for the Portuguese community O Jornal on an academic conference inspired by the fiftieth anniversary of Capelinhos (Portuguese language article here)
50th anniversary of the Capelinhos volcano in the Azores – speech by the American ambassador to Portugal, 27 September 2007, to mark the beginning of the 50th anniversary commemorative events

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J. Logan Lobley’s ‘Mount Vesuvius’ (1889) 1 April 2008

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A nineteenth-century volcanological work available for free and in full via the Internet Archive‘s American Libraries project: J. Logan Lobley, Mount Vesuvius. A Descriptive, Historical, and Geological Account of the Volcano and its Surroundings (London: Roper & Rowley, 1889).

Mount Vesuvius, the world-famed volcano of Southern Italy, has been for many centuries an object of great interest to the inhabitants of Europe. In ancient times, the conspicuous position of the mountain in one of the fairest and most frequented portions of the Roman dominions – the resort of the most wealthy, most famous, and most noble of the citizens of Rome – and the terrible character and dreadful results of the eruption of the year 79, combined to render Vesuvius an object of especial interest and wonder.

List of chapter headings: I: The Neapolitan volcanic region. II: The surroundings of Vesuvius. III: The mountain. IV: History to 1850. V: History: 1851-1868. VI: History: 1869-1888. VII: Geology of Vesuvius. VIII: Volcanic action. IX: Volcanic products. X: The minerals of Vesuvius. XI: The flora of Vesuvius.

The author was Professor of Physiography and Astronomy at the City of London College, and author of Geology for All (1888) among many other things.

Read Mount Vesuvius, in a choice of formats, here.

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Volcanoes, Basalt, and the Discovery of Geological Time: an online exhibition 30 March 2008

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‘Vulcan’s Forge and Fingal’s Cave: Volcanoes, Basalt, and the Discovery of Geological Time’ was an exhibition presented at the Linda Hall Library, Kansas City, Missouri, from October 2003 to March 2004. Why tell you about an exhibition that closed four years ago? Because, thanks to the LHL’s enlightened and imaginative approach to the internet, it left a wonderful website behind it.

The exhibition presented over sixty rare books and journals from the period 1650-1830, representing changing perceptions of basalt and the significance of the understanding of basalt’s igneous (as opposed to aqueous) nature and of the phenomenon of volcanism for the growing recognition of the immensity of geological time. The online exhibition is divided into seventeen richly-illustrated sections which display sixty-six printed items dealing with basalt and volcanism, many of them spectacular and beautiful as well as fascinating. The presentation of these items is crystal-clear and immaculate, the texts are informative and thought-provoking, and the organization and navigation is straightforward.

Vesuvius and EtnaBasalt along the RhineDerbyshire Toadstone … it’s all here. Highly recommended.

Vulcan’s Forge and Fingal’s Cave – entrance page for the online exhibition
Online Exhibitions – Linda Hall Library – list of the online exhibitions available at the LHL
Linda Hall Library of Science, Engineering & Technology – main page for the LHL

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1908 ascent of Mt Erebus recalled 10 March 2008

Posted by admin in anniversaries, Antarctica, Erebus, history of volcanology, volcano culture.
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On 10 March 1908 members of the British Imperial Antarctic Expedition (also known as the Nimrod Expedition) climbed the active Antarctic volcano Mount Erebus on Ross Island, the first people to make the ascent to the crater rim. The 100th anniversary of this achievement is being marked today at the Mount Erebus Volcano Observatory, which is run by New Mexico Tech at the very un-Antarctic location of Socorro, New Mexico.

Smithsonian Institution Global Volcanism Program – summary information for Mount Erebus
MEVO – Mount Erebus Volcano Observatory
Antarctic Explorers: Ernest Shackleton – detailed biography, includes an account of the Nimrod Expedition

Erebus ascent recalled – Stuff.co.nz, 10 March 2008

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The life history of a volcano: a lecture from 1891 22 February 2008

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A Geological Study.

[From The Leeds Mercury, 30 May 1891, p. 5]

At the meeting of the Leeds Geological Association on April 21st, in the absence of Mr. S. Chadwick, F.G.S., who was announced to read a paper on “Flint from the Yorkshire Chalk,” a lecture on “Volcanoes” was given by the Hon. Secretary (Mr. W. L. Carter, M.A., F.G.S.) illustrated by a number of beautiful lantern slides.

What is a volcano? The old answer was, “A burning mountain, from the summit of which issue flames and smoke.” This, the lecturer said, was a misconception from beginning to end. A volcano is essentially an opening in the earth’s crust communicating with the heated interior. The volcanic mountain is the mass of materials which has been ejected from this aperture. A volcano does not burn, “i.e.,” there is no combustion at the summit, but it emits large quantities of steam and fine ash, which together form the so-called smoke, and streams of white hot lava, the flashing light from which reflected by the overhanging clouds looks like flame. The name “volcano” comes from the Island of Vulcano, near Sicily, which was styled by the ancients “The Forge of Vulcan.” This volcano is now fairly quiescent, and a chemical works was established in the crater some years ago, by an enterprising Scotch firm, for the condensation of the sulphurous and other chemical gases which it gave off. One night, however, an eruption took place, blowing the manufactory into the air, and effectually stopping that branch of industry. One naturally turns to Italy for examples of volcanoes, because it is easily accessible, and illustrations of all stages of volcanic action are found there. There are three Italian volcano districts — (1) the Roman, in which there is no active vent, but perfect craters and great crater lakes; (2) the Sicilian; and (3) the Neapolitan, both of which are partly terrestrial and partly marine. With regard to the supposed connection of the sea with volcanic action, as a source of water-supply, it is interesting to note that the two regions which still touch the sea are active, whilst the Roman region, which has been separated from it by the advance of the coast-line, is extinct.

Formation of the volcano.

One especially good instance of the birth of a volcano has been recorded by four eye-witnesses. In September, 1858 [sic: clearly an error, the correct date is 1538], Monte Nuovo, a hill 430 feet high, and 8,000 feet in circumference, was raised in three days on the shore of the Bay of Naples. There had been earthquakes for two years, which increased in frequency, when a fissure was formed which emitted springs, first of cold and then of boiling water. On Sunday night, September 29th, the earth suddenly burst open, and great quantities of ashes mixed with water were ejected, covering the country for miles round, and the sea retreated for some distance. No lava issued from the cone, which was entirely composed of ashes; and there has been no eruption on the same spot since. Thus is formed the simple volcanic cone. Passing on to more mature stages of volcanic existence, we will take Vesuvius as an example. In prehistoric times, this mountain would have formed a perfect cone, the top of which, being blown away, produced the wide crater-plain which existed up to A.D. 79. Previously there is a no record of volcanic activity, but in that year the western side of the old volcano was blown away, and a new cone formed. By this eruption Pompeii and several other towns in the district were destroyed. Since then the volcano has been in constant activity. Vesuvius is divided into several zones. The lower cultivated slope, merging into the plain, is composed of disintegrated volcanic rock, and is very fertile. This extends to 1,500ft. above the sea-level. The Desert Platform, a barren and desolate waste continually invaded by fresh lava streams, reaches from 1,500ft. to 2,500ft. On the eastern side is the ridge of Monte Somma, which half encircles the active vent, and is part of the original cone destroyed by the eruption of A.D. 79. The present cone is three miles in circumference, and 1,500ft. in height above the Desert Platform. The summit alters with every eruption, and smaller secondary cones are formed inside the chief crater. Etna is a more complex example of the colossal volcano. It is 10,840ft. above sea-level, and there are several zones of vegetation between the base and the desert region. There you see nothing but scoriae, lava, and snow. The great height of this cone causes the hydrostatic pressure in the central pipe to be too great to allow of the lava now reaching the central crater; and by the yielding of the sides, parasitic or daughter cones are formed. At subsequent stages in the existence of a volcanic cone the ground underneath becomes fissured, and an easier vent for the volcanic forces being thus provided, small cones or puys are formed in the plain around the base of the volcano.

The Eruption.

As an example of a great eruption, we may take that of Vesuvius in 1872, in which several adventurous tourists lost their lives. The flow of lava was so profuse that Professor Palmieri wrote — “The cone seemed completely perforated, and lava oozed, as it were, through its whole surface. I cannot better express it than by saying — Vesuvius sweated fire.” Terrific discharges took place from the summit, ejecting enormous quantities of steam and ashes, reaching 5,000ft. above the top of the mountain, which were carried slowly along by upper air currents. Darkness was produced over a considerable area, and the rain of ashes devastated the crops and caused great alarm. One lava stream on the western side carried away large portions of two villages and so rapid was its flow that the villagers were barely able to save their portable possessions, and some lost everything. The decadence of the eruption was accompanies by a storm of thunder and rain, which brought down the hurtful gases and salts from the great cloud, shrivelling up grass, vines, and trees. Eruptions are not, however, always so violent as this, and in the case of Stromboli the sequence of events can be watched at close quarters without danger. Stromboli is a volcanic cone near Sicily, which rises out of the Mediterranean to a height of 3,090ft. and has been in constant activity for at least 2,000 years. The crater is in the side of the mountain, and from it clouds of vapour issue continually. The outbursts occur at intervals of from one to twenty minutes, and are unequal in intensity. By care an observer can climb to a point above the crater and watch the eruption. The black slaggy bottom of the crater is traversed by fissures, from which many jets of vapour curl quietly up. From larger apertures bursts of steam take place at intervals and molten rock wells out. In other openings a viscid substance is seen slowly heaving up and down, until a gigantic bubble is formed, which, bursting violently, sets free a great mass of steam, which carries great fragments of the molten rock high into the atmosphere. Thus in this working model, as it were, of a volcano, we see the essentials of all volcanic eruptions: — 1. The existence of apertures communicating with the interior of the globe. 2. The presence of lightly heated matter beneath the surface. 3. Great quantities of subterranean water, which by contact with this molten rock becomes suddenly converted into steam. These three conditions explain eruptions alike on the smallest and the largest scale.

Products of Eruption.

Many vapours are given off by a volcano, including acid gases, such as chlorine, hydrochloric acid, and sulphurated hydrogen. In less active stages carbonic acid is emitted in large quantities. Steam, however, is the most important vaporous product of volcanic action, forming 990-1000ths of the whole cloud. It has been calculated that during an eruption at Etna, which lasted one hundred days, that the steam emitted each day would, if condensed, have produced four and a half million gallons of water. Thus we cannot be surprised that floods of water play a considerable part in the devastation which accompanies a volcanic eruption. These water floods are produced either by the condensation of steam, or by the melting of masses of snow, owing to the rapid rise in temperature, or by the disruption of subterranean reservoirs. An instance of the last was seen in Java in 1817, when a lake of hot, acid water, filling a large crater, was suddenly discharged, with frightful destruction. Water rushing down the cone collects the volcanic dust, and forms a mud lava, which afterwards consolidates into tuff. It was by such a mud lava that Herculaneum was engulfed in A.D. 79. Various fragmentary materials are ejected by the force of an eruption. The finest of these form a light grey powder called ashes, though they are not products of combustion. So fine is this ash that Mr. Whymper estimated that though two millions of tons were ejected in one eruption of Cotopaxi, there would be from 4,000 to 25,000 particles in each grain weight. During an eruption in Nicaragua in 1835, there was darkness over an area of thirty-five miles in radius; the ground twenty-four miles from the mountain was covered ten feet deep, and the ash fell 700 miles from the centre of eruption. Larger fragments, from the size of a pea to that of a walnut, and great blocks, are often ejected from volcanoes. In Java, in 1772, a vally nine miles long was filled with angular blocks to a depth of 50 feet. Volcanic bombs, which are lumps of lava, rounded by rapid rotation as they move through the air, are found in almost all sizes. Lava is molten rock resembling slag. It is white hot at its exit from the crater, but soon becomes a dull red. Lavas differ in liquidity according to the amount of the included steam, and also according to their chemical composition and temperature. Viscous lavas give off very little steam and take on ropy structure owing to the crinkling of the cooling surface by the continued movement of the lower layers. Liquid lavas give off much steam, are rapid in flow, and form a sharp, cindery surface. Trachytic (basic) lavas from thin, widely extended sheets. The enormous size of some lava streams may be estimated from the fact that the flow from one eruption in Iceland would form a mountain greater than Mont Blanc.

Volcanic Decrepitude.

Having thus dealt with the mature and vigorous volcano, it remains to enumerate the characteristic of its declining strength. These consist largely of vaporous emanations. A notable instance is that of the Solfatara, a crater in the Phlegraean (Burning) Fields to the north of Naples. It evolves gases and sulphurous fumes, depositing pure sulphur. Its last eruption was in 1198. Geysers (gushers), which are eruptive fountains of water and steam, exist in areas of decaying volcanic activity. Sinter cones and terraces are also formed by the emission of hot springs holding silica in solution. At a further stage carbonic acid gas alone is given off, as in the case of the Dog’s Grotto near Naples. Extinct craters are found in many parts of the world, and there are many examples in the Phlegraean Fields. The largest is Astroni, which is one mile in diameter, having in the centre a boss of trachytic rock, which probably is the plug of the old vent. Now the crater is overgrown with oaks and undergrowth, and is used as a Royal preserve for hunting wild boar and other big game.

Dissected Volcanoes.

The action of atmospheric agencies on extinct volcanic cones gradually lays bare their innermost parts, and reveals many interesting details of structure. There have been in times past several volcanoes in Britain larger than Etna. The Mull volcano, which was once upwards of 12,000ft. in height, is now reduced to a group of hills about 3,000ft. high. In Skye there is the wreck of a similar colossal cone, and Ben Nevis is carved from the inner masses of another such mountain. Arthur’s Seat, Snowdon, and Cader Idris are also formed of volcanic rocks. That volcanic action is not yet entirely spent in the British area is evidenced by hot springs and earthquakes. The hot spring at Bath, for instance, pours forth daily 180,000 gallons of water at 120 degrees Fahrenheit, and it is said that the materials which it has brought to the surface in solution during the last 2,000 years would be sufficient to form a cone as large as Monte Nuovo. Earthquake shocks are also occasionally felt in our country, such as that which did so much damage in Essex and Suffolk a few years ago, showing the existence of pent-up forces beneath the surface. The successive stages in the existence of a volcano have thus been traced from its earliest commencement in a mere fissure, around which a simple cone was built up, to a colossal volcano such as Etna, with numerous daughter cones. From this period of full maturity we have followed the fiery giant into a state of decrepitude, when he is able to fume and nothing else. Then comes the period of extinction, and as time goes on the cone is broken down by atmospheric denudation until its hidden framework is brought to light, and entering nature’s dissecting-room we are able to study the anatomy of the volcano, and thus many of the mysteries of its life history are made clear to us.

An interesting discussion followed, in which Messrs. Thrippleton, Jefferson, Bedford, and the President took part, and the thanks of the meeting were unanimously given to the lecturer, and to Mr. Bedford for his management of the lantern. A hearty vote of thanks also was accorded to those who had lent lantern slides, and especially to Mr. Branson for a splended series of Italian views.

The Volcanism Blog

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